A work in progress that is shaping up to be a great romp.
Each class has two subclasses, with a single different skill tree depending on which one you pick. You get skill points by leveling and completing achievements, such as a certain number of total kills. These points can be used to buy and level different skills.
Death is handled very interestingly in this game. You have 3 lives in each mission. If you die 3 times your warrior goes to the "Sanctuary" From there you can attach them to equipment to level it up, pay a small fee to revive them, or use them as a brutal AOE with another character. It is actually interesting to see people leveling up warriors just to kill them for their AOEs. You can have 12 characters at one time, and can switch between them on the fly from the lobby.
All in all it is a great game with some huge bugs. The truth of the matter though is that it's been out for less than a month. WoW is the accepted standard, so look back at the WoW launch. How long did it take them to fix their bugs? Last time I checked they still patch the game on Tuesdays...